1. Field of the Invention
The present invention relates to parts installation structures and their manufacturing methods, and more particularly to a printed circuit parts installation structure for a membrane switch and its manufacturing method.
2. Description of the Prior Art
In recent years, many electronic devices have been developed. Printed-circuit boards are indispensable in a significant portion of these electronic devices.
When printed-circuit boards appeared on the market, the terminals of electronic parts, such as the semiconductor parts, were inserted in small holes, which opened to the wiring pattern of printed-circuit board. Then the printed-circuit board was dipped in a dip-tank of solder. The terminals and the wiring pattern were soldered, and the electronic circuit was assembled. However, quite recently, electronic parts were miniaturized. The method of installing electronic parts on printed-circuit boards has changed. For instance, a paste solder may be applied at fixed portions of the wiring pattern of the printed-circuit board. Then, the terminals of electronic parts, such as transistors, are brought into contact with the fixed portions, and the paste solder is melted by an infrared heating machine etc. Soldering is thus achieved between the terminals of electronic parts.
In recent years, membrane switches have been used for the switches of keyboards in personal-computers etc. In miniaturizing the keyboard, the membrane switch is helpful. Moreover, the electronic parts such as large-scale ICs and luminescence elements may be connected to the wiring pattern of a membrane switch substrate.
FIG. 2 is a cross-sectional view, showing a conventional technique for mounting electronic parts (d) on a membrane switch. The leads d' of the electronic part (perhaps a chip diode) d are fixed by a conductive adhesive (c) to a printed wiring pattern (b) on a switch sheet (a). A sealing member (e) formed of a UV stiffening material covers the membrane switch sheet (a) and the chip diode (d).
In the mounting of the parts mentioned above, the chip diode (d) is adhered onto the membrane switch sheet (a) and is covered by the sealing member (e). Therefore, the overall device becomes thick, unsuitable for use in a thin keyboard.
Moreover, both of the printed wiring pattern (b) and the electronic parts are covered by the sealing member (e). Therefore, when the printed wiring pattern (b) and the electronic parts cover a large area, a lot of sealing material is needed. The UV rays do not reach the lower side of electronic parts (d), and the UV rays do not stiffen the sealing material. To compensate for this, the membrane switch sheets are inserted into a furnace for the stiffening the sealing materials.
In addition, when a large force is applied between the membrane switch sheet (a) and the sealing member (e) or electronic parts (d), the printed circuits, which consume substantial area on the membrane switch sheet (a), may receive a large amount of damage, and the sealing number (e) or the electronic parts (d) may peel off of the membrane switch sheet (a).
In view of the aforesaid drawbacks associated with conventional parts installation structures and their manufacturing methods, it is an object of the present invention to provide a thin parts installation structure and a manufacturing method therefor.
Another object of the present invention is to provide a manufacturing method that easily stiffens adhesive materials for membrane switch keyboards, without the need for a UV stiffening process.
A further object of the present invention is to decrease the equipment cost for parts installation structures and the manufacturing method therefor.